Pressure Relief nozzle

ABSTRACT

A pressure relief nozzle installs on the face of a drill bit, and provides a flow path for drilling fluid. The pressure relief nozzle has a larger internal flow area when flow rates through the drill bit are high, and a smaller flow area when flow rates are low. Upon reduction of the pressure relief nozzle&#39;s internal flow area, the pressure drop across the drill bit tends to stabilize due to the reduced flow area through the drill bit.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to drill bits. More particularly,embodiments of the invention relate to fluid nozzles installed on drillbits. Even more particularly, embodiments of the invention aremulti-use, self-adjusting pressure relief nozzles.

2. Description of the Related Art

FIG. 1 includes a drilling installation having a drilling rig 10 at thesurface 12 of a well, supporting a drill string 14. The drill string 14is an assembly of cylindrical drill pipe sections which are connectedend-to-end through a work platform 16. A drill bit 32 connects to thelower end of drill string 14. A borehole 18 extends through earthformations 20 and 21.

As the drill bit 32 rotates, drilling fluid is pumped from a mud pit 34at the surface through a hose 37, into the drill string 14, and to thedrill bit 32. The drill bit 32 ejects drilling fluid through nozzlesinstalled on the face of the drill bit. The drilling fluid cools andlubricates the drill bit 32 and removes cuttings from the borehole 18.The drilling fluid then rises back to the surface through the annulararea between the drill string 14 and the walls of the borehole 18. Atthe surface, the fluid is collected and returned to the mud pit 34 forfiltering.

Two types of drill bits are generally used, roller cone bits and fixedcutter bits. In both types of drill bits, an interior cavity holds thedrilling fluid. The drilling fluid arrives to the cavity via the drillstring and is ejected through nozzles installed on the face of the drillbit.

A layout of a three-cone rock bit is shown in FIG. 2. A roller cone bit32 includes a threaded pin end 14 and is configured with a number ofroller cones 16, typically three, at its bottom that are equidistantlyspaced around the circumference of the bit. The cone shells 18 areimbedded with inserts 19 (also described as cutting elements or teeth)arranged in annular rows on the cone that penetrate the formation as thedrill bit rotates in the hole. Generally, between each pair of cones isa nozzle receptacle 35 with an installed erosion resistant nozzle 30that directs the fluid from the exit of the nozzle 34 to the hole bottomto move the cuttings from the proximity of the bit and up the annulus tothe surface. Additional nozzles may be located elsewhere. The placementand directionality of the nozzle receptacles and nozzles, as well as thenozzle sizing and nozzle extension, significantly affect the rate ofpenetration for the drill bit and bit life.

A fixed cutter bit, also referred to as a drag bit, does not have rollercones but instead has rows of cutting elements arranged on its face. Anexample of a fixed cutter bit is shown in FIG. 3. Bit 32 generallyincludes a bit body having shank 13. Bit 32 further includes a cuttingstructure on the face 14 of the drill bit, preferably including variousPDC (polycrystalline diamond compacts) cutter elements. Nozzles areplaced on the face of the fixed cutter bit in order to distribute anddirect drilling fluid to specific regions and or locations of a bit.

Optimizing the performance and life of a drill bit depends on anenormous number of variables, including variables that change during thedrilling program. One variable of particular interest to the inventionis the hydraulic pressure of the drilling fluid and the flow of drillingfluid at the drill bit. Controlling the pressure drop across the drillbit may be desirable for a number of different reasons, and under anumber of different conditions.

One difficulty encountered in drilling a borehole, especially for deepwells, is the need to maintain system pressure losses at a value belowthat of a rig's pressure rating. In deep wells, system pressure lossesincrease due to drill string length. System pressure loss is the sum ofthe pressure losses due to fluid flow through surface equipment, drillstring, drill bit and wellbore annulus. In such situations of increasedsystem pressure loss, because a rig has a fixed stand pipe pressurerating, flow rate is decreased, to keep the pressure losses below thatof the rig's constant pressure rating.

A situation where maintaining a specific pressure drop across a drillbit is desirable is where a drilling tool depends on the pressure dropat the bit. For example, in a long, stepped-out well, the drill stringcan no longer be pushed along the borehole wall; the friction created bythe sliding motion of the drill string against the borehole wall is toogreat. In such situations, slide mode drilling, needed for wellboretrajectory changes, is almost impossible due to the high wellbore dragvalues. Rotary steerable tools, which enable constant drill stringrotation (no slide mode drilling) even when making wellbore trajectorychanges, are much more effective in such instances. Certain types ofrotaty steerable tools require a specific narrow range of pressure dropvalues below the tool to make them effective, however. Pressure dropvalues above and or below the specific value or range lead to toolineffectiveness or inability to achieve required dog-legs. If thepressure drop is too low, there is not enough energy provided the toolfor it to operate properly. If the pressure drop is too great, the sealsin the tool are damaged. Consequently, where the pressure drop below therotary tool does not fall in the required narrow range, the entire drillstring must be removed or “tipped” from the well bore, section bysection. New nozzles may then be installed on the face of the drill bitto change the pressure drop across the drill bit.

Increased system pressure losses compromise the efficiencies of rotarysteerable tools and bit performance in applications needing specifiedpressure losses. In the case of rotary steerable drilling when nozzleflow areas are kept constant, and at reduced flow rates, the pressuredrop across the bit and the efficiency of the rotary steerable tool arecompromised. The pressure drop across the bit makes up the largemajority of the pressure drop below the tool. If the pressure dropacross the bit can be held to values that permit the operation of therotary steerable tool, it will be to great advantage to the success ofthe drilling program. It would also avoid the need to trip the drillstring, which is very time consuming and therefore expensive.

Another situation where fluid pressure is important is for the cleaningof cutting elements on a drill bit. Cutting elements in plastic shaleand other formations tend to suffer from a phenomenon known as “bitballing”. As is known in the art, bit balling describes the packing offormation between components of the drill bit while cutting formation,such as between the cutting elements. When it occurs, cutting elementscan become packed off so much that they don't penetrate into theformation effectively, tending to slow the rate of penetration for thedrill bit.

Fluid directed toward the cones of a roller cone bit, or the blades andor cutters of a PDC or drag bit, can help to clean the cutting elements,thus maintaining or improving the rate of penetration for the bit. Aminimum hydraulic horsepower per square inch of borehole area isrequired, however, in order to clean the cutting elements adequately. Adrop in fluid pressure across the drill bit results in a drop inhydraulic horsepower at the bit, leading to poor cleaning of the drillbit's cutting elements. Similarly, hydraulic horsepower at the bitaffects the fluid hydraulics at the bottom of the borehole and mayadversely affect the drilling fluid's ability to remove cuttings fromthe borehole efficiently.

There thus is a need for an innovation that can help maintain therequired pressure drop across a drill bit, regardless of well depth andor departure, without over compromising the flow rates needed toeffectively clean drill bits. Such an innovation, should also apply toany tool or application, where performance is pressure dependent.Ideally, it would be compatible with conventional components used indrilling a wellbore.

SUMMARY OF THE INVENTION

The invention includes various types of pressure relief nozzles andmethods for using them. One or more pressure relief nozzles install onthe face of a drill bit, and provide a flow path for drilling fluid. Thepressure relief nozzle has a larger internal flow area when flow ratesthrough the drill bit are high, and a smaller flow area when flow ratesare low. This response coincides with an increase in the system pressurelosses, as flow rate is reduced at greater depths and departures. Uponreduction of the pressure relief nozzle's internal flow area, thepressure of the drilling fluid tends to stabilize because the total flowarea through the drill bit has been reduced. The reduced flow area ofthe nozzles helps maintain the pressure needed for rotary steerabledrilling and in applications that are dependent on high hydraulichorsepower per square inch (HIS) values.

A pressure relief nozzle according to embodiments of the inventioninclude a hollow nozzle body having an interior passage defining a fluidflow path, and a movable flow control member located in the fluid flowpath. The movable flow control member moves between positions, includinga fully open position and a fully closed position (although the fullyclosed position may or may not cut off fluid flow).

In one embodiment, the movable flow control member may be a pluginserted in the nozzle body. The plug moves linearly with respect to thenozzle body to reduce or increase flow area. The pressure drop acrossthe nozzle or bit, based on flow rates, is affected.

In another embodiment, the movable flow control member includes a set ofone or more sliding ramps that move laterally with respect to the nozzlebody to reduce and increase fluid flow through the pressure reliefnozzle.

Other embodiments of the invention include drill bits with at least onepressure relief nozzle that changes its internal flow area in responseto changes in flow rate and at least one conventional nozzle that doesnot change its internal flow area in response to changes in flow rate.Methods for operating such a drill bit are also within the scope of theinvention.

Thus, the invention has a combination of features and advantages thatenable it to overcome various problems of prior devices and methods. Thevarious characteristics described above, as well as other features, willbe readily apparent to those skilled in the art upon reading thefollowing detailed description of the preferred embodiments of theinvention, and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the preferred embodiment of thepresent invention, reference will now be made to the accompanyingdrawings, wherein:

FIG. 1 is a cut-away view of a wellbore being drilled;

FIG. 2 is an external view of a rolling cone rock bit;

FIG. 3 is an external view of a drag bit;

FIG. 4 is an external view of a base according to a first embodiment ofthe invention;

FIG. 5 is an external view of a nozzle body that mates to the base ofFIG. 4;

FIG. 6 is a schematic view of the first embodiment of the invention in aclosed position;

FIG. 7 is a cut away view of a nozzle plug inserted into a nozzle body;

FIG. 8 is a schematic view of the first embodiment of the invention inan open position;

FIG. 9A is a schematic view of a second embodiment of the invention;

FIG. 9B is a top view of a third embodiment of the invention;

FIG. 9C is a top view of a fourth embodiment of the invention; and

FIG. 10 is a flow diagram showing a method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As used herein, the term “closed” refers to and is defined as thepressure relief nozzle in its minimum flow condition even if some fluidis still allowed to flow through the nozzle. The term “fully closed”refers to a no flow, zero flow condition. The term “fully open” refersto and is defined as the pressure relief nozzle in its maximum flowcondition. The term “open” refers to and is defined as the pressurerelief nozzle in other than a “closed” or “fully closed” position. Itshould be noted that these terms should still be viewed in context andmay not fully apply when, e.g., using relative terminology such as “moreclosed” or “more open”.

One of the locations of pressure loss for the drilling system is acrossthe drill bit. A smaller total low area through the drill bit, i.e. forthe fluid ejected from the drill bit, results in higher pressure lossacross the drill bit, all else being equal. This can be used to affectthe pressure drop across the drill bit when fluid flow rates arereduced.

The pressure relief nozzle of the invention opens to increase flow area,when flow rates are high. The pressure relief nozzle closes, restrictingflow area, and establishing the required pressure drop, when flow ratesare reduced. The nozzle is capable of repeated opening and closing inresponse to increases and decreases in flow rate.

Pressure drops across a drill bit are proportionate to the square of theflow rate, and are inverse to the total flow area (TFA) through thedrill bit. When the self-adjusting pressure relief nozzle of theinvention closes, either fully or partially, the TFA through the drillbit is reduced. The reduction in TFA partially compensates for thereduced pressure drop that will have occurred if the flow area was keptconstant. Thus, the pressure drop across the bit may be kept close toconstant, such as within 5% or 10% for a given reduction in flow rate.This maintenance of the pressure drop may require a plurality ofpressure relief nozzles installed in the drill bit.

In operation there may be five nozzles installed on the face of a drillbit, only one or two constructed to be a pressure relief nozzle of theinvention. As drilling begins, there may be 1,000 gallons of drillingfluid per minute being pumped through the drill bit, and the TFA may beone square inch. The pressure drop across the bit may be 750 psi. As thedrilling proceeds and goes deeper, the pressure losses increase. Asfluid flow is reduced in response to increased pressure losses, fluidflow may be cut to 800 gallons per minute. Total flow area may bereduced to 0.7 square inches by the contraction in flow area in thepressure relief nozzles. The pressure drop across the drill bit would beapproximately the same as it was before.

A first embodiment of a self-adjusting pressure relief nozzle includes anozzle body and a nozzle plug inserted into the nozzle body. Referringto FIG. 4, a plug 404 includes a head 406 and a base 402. Base 402includes holes 408 at its lower end that facilitate the flow of drillingfluid through the pressure relief nozzle when it is in an open or fullyopen position. Plug 404 inserts into the nozzle body to form the firstembodiment of a pressure relief nozzle.

An external view of a nozzle body 500 according to the first embodimentis shown in FIG. 5. Nozzle body 500 has an upper end 502 (the body 500being in an inverted position). Upper end 502 includes threads 504suitable to engage a standard nozzle receptacle in the face of a drillbit. Other mating structures may of course be used. Body 500 alsoincludes a lower portion 506. Lower portion 506 includes an opening 508sized to accept nozzle plug 404. Plug 404 locks into opening 508 by anyappropriate means, e.g. suitable complementary geometries between thebase of the nozzle plug 404 and the opening 508.

FIG. 6 shows a fully closed position for the first embodiment. Plug 404having base 402 and head 406 inserts into nozzle body 500. Nozzle body500 is hollow and includes an interior passage 608 with interior surface602 that defines a fluid flow path. Head 406 abuts against the interiorsurface 602 of hollow nozzle body 500 to form a liquid-tight sealagainst passage 608 when in the fully closed position. Consequently, theminimum diameter of this embodiment's fluid flow path is zero when thenozzle plug is in the low flow condition.

Referring to FIG. 7, head 406 slides vertically (linearly) relative tobase 402 by opposing hydraulic load 702 and spring forces 704. In theabsence of a hydraulic load, spring 706 forces the head 406 to a fullyextended position relative to base 402. Upon the application of asufficient hydraulic load to the head 406, the head is compressed towardthe base 402, opening the pressure relief valve. In this embodiment, thelinear sliding of the head 406 relative to the base 402 opens and closesthe pressure relief valve. The amount of hydraulic load necessary tocompress head 406 toward base 402 may be adjusted by selection of springstrength.

FIG. 8 shows a fully open position for the first embodiment. As isappreciated by those of ordinary skill in the art, drilling fluid flowsaccording to a pressure gradient, from a high pressure location to a lowpressure location. The magnitude of the hydraulic load is thereforeestablished by the difference in fluid pressures above and below thepressure relief nozzle. Sufficient hydraulic load 702 removes head 406from the interior surface 602 of hollow nozzle body 500. Drilling fluid810 then flows through the pressure relief valve. If the head of thenozzle plug is forced an adequate distance from its seating locationagainst the interior passage, the flow area of the nozzle is that of theinterior passage of the nozzle when the nozzle plug is in a high flowlocation.

A second design of a pressure relief nozzle is shown in FIG. 9A. Nozzlebody 902 includes interior passage 911 that forms a fluid flow path 903.Base 904 supports sliding ramps 906. Springs 910 attach between slidingramps 906 and shoulder 908 formed in nozzle body 902. Low pressure flowdiameter 912 and high pressure flow diameter 914 are also shown.

Low flow diameter 912 is the minimum diameter of the fluid flow pathwhen the pressure relief nozzle is operating under low flow conditions.High flow diameter 914 is the minimum diameter of the fluid flow areawhen the pressure relief nozzle is operating under high flow conditions.In other words, although greater in area than low flow diameter 912,high flow diameter 914 is smaller than interior passage 911. Diameter914 is the location of minimum flow area in the pressure relief nozzlewhen the nozzle is under high flow conditions. Under highflowconditions, the sliding ramps move laterally outward from theinward, closed position of the low fluid flow condition. As the flowrate is reduced, the sliding ramps move laterally inward from anoutward, more open position. Thus, in this embodiment, the lateralsliding of the ramps 906 relative to the base 904 opens and closes thepressure relief valve. The amount of fluid pressure (hydraulic, load)necessary to open the valve may be adjusted by selection of springstrength. It will be appreciated that similar results could be obtainedeven if only a single sliding ramp were employed.

Several ramps of different geometries can be used to achieve the sameeffects. Referring to FIG. 9B, the flow path may include an opening, forexample, at its center that opens from a smaller flow area A at itscenter under low flow conditions to a larger flow area, at B, under highflow conditions. As another example, a “pie slice” area of the flow pathmay slide open under high flow rate conditions and slide close under lowflow rate conditions, as generally shown in FIG. 9C.

A drill bit designed according to the principles of the invention has asmaller TFA at lower flow rates than higher flow rates. The exactrelationship between TFA and flow rates, and the layout and number ofpressure relief nozzles on the face of the drill bit, may be left to thedrill bit designer of ordinary skill and will vary depending on thedrilling program and the requirements of, e.g., a given rotary drillingtool. In each case, however, a reduction in TFA in response to a lowerflow rate tends to moderate the variation in pressure drop across thedrill bit.

From the perspective of an operator, the controllable variable is flowrate of the drilling fluid. A method according to the invention includesthe repeated opening and closing of a drill bit nozzle based upon flowrate of drilling fluid through the drill bit. Referring to FIG. 10, atstep 1010 a pressure relief nozzle is installed in a drill bit. At step1015, the flow rate increases and the pressure relief nozzle opens froma smaller minimum diameter to a larger minimum diameter. This may be theinitial pumping of drilling fluid through the drill bit. At step 1020,the pressure relief nozzle closes from a larger minimum diameter to asmaller minimum diameter. At step 1025, flow rate again increases andthe pressure relief nozzle reopens from the smaller minimum diameter tothe larger minimum diameter.

While preferred embodiments of this invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit or teaching of this invention. Theembodiments described herein are exemplary only and are not limiting.Many variations and modifications of the system and apparatus arepossible and are within the scope of the invention. Accordingly, thescope of protection is not limited to the embodiments described herein,but is only limited by the claims which follow, the scope of which shallinclude all equivalents of the subject matter of the claims.

1. A pressure relief nozzle, comprising: a hollow nozzle body having anupper end, a lower end, and an interior passage connecting said upperend to said lower end and defining a fluid flow path for fluid flowingthrough said interior passage; a flow control member located in saidfluid flow path, said flow control member movable between a firstposition and a second position, dependent upon a difference in fluidpressure of said fluid at said upper end and said lower end of saidnozzle body.
 2. The pressure relief nozzle of claim 1, said upper endincluding means for connecting said nozzle body to a nozzle bore in adrill bit body.
 3. The pressure relief nozzle of claim 1, said firstposition being a fully open position and said second position being afully closed position.
 4. The pressure relief nozzle of claim 1, saidflow control member being a plug inserted in said nozzle body.
 5. Thepressure relief nozzle of claim 1, said flow control member movinglinearly with respect to said nozzle body to move from said firstposition to said second position.
 6. The pressure relief nozzle of claim1, said flow control member moving laterally with respect to said nozzlebody to move from said first position to said second position.
 7. Thepressure relief nozzle of claim 6, said flow control member including aramp.
 8. The pressure relief nozzle of claim 6, said flow control memberincluding a sliding ramp.
 9. The pressure relief nozzle of claim 6, saidflow control member including a first ramp and a second ramp.
 10. Thepressure relief nozzle of claim 6, said flow control member including afirst sliding ramp and a second sliding ramp.
 11. The pressure reliefnozzle of claim 1, said first position allowing fluid flow through saidpressure relief nozzle and said second position not allowing fluid flowthrough said pressure relief nozzle.
 12. The pressure relief nozzle ofclaim 1, said first position defining a first diameter for said interiorpassage and said second position defining a second diameter for saidinterior passage, said first diameter being larger than said seconddiameter.
 13. The pressure relief nozzle of claim 1, said flow controlmember being repeatedly movable from said first position to said secondposition, and from said second position to said first position.
 14. Thepressure relief nozzle of claim 13, said first position defining a firstdiameter for said interior passage and said second position defining asecond diameter for said interior passage, said first diameter beinglarger than said second diameter.
 15. The pressure relief nozzle ofclaim 1, said flow control member controlling a flow area for said fluidflow path, said first position providing a larger flow area than saidsecond position.
 16. A method for operating a pressure relief nozzle,comprising; installing a pressure relief nozzle to a drill bit body,said pressure relief nozzle having a fluid flow passage, said fluid flowpassage having a first minimum diameter and a second minimum diameterdependent upon a pressure of fluid in said fluid flow passage, saidfirst diameter being smaller than said second diameter; opening saidpressure relief nozzle from said first diameter to said second diameter;and closing said pressure relief nozzle from said second diameter tosaid first diameter.
 17. The method of claim 16, further comprising:re-opening said pressure relief nozzle.
 18. The method of claim 17, saidpressure having an initial value and staying within ten percent of saidinitial value throughout said opening, closing, and re-opening steps.19. The method of claim 17, said pressure having an initial value andstaying within five percent of said initial value throughout saidopening, closing, and re-opening steps.
 20. The method of claim 16,further comprising: installing a second pressure relief nozzle to saiddrill bit body; said second pressure relief nozzle having a second fluidflow passage, said second fluid flow passage having a first minimumdiameter and a second minimum diameter dependent upon said pressure offluid in said second fluid flow passage, said first diameter of saidsecond fluid flow passage being smaller than said second diameter ofsaid second fluid flow passage; opening said second pressure reliefnozzle from said first diameter to said second diameter; and closingsaid second pressure relief nozzle from said second diameter to saidfirst diameter.
 21. The method of claim 16, further comprising:increasing fluid flow through said fluid flow passage from an initialflow value simultaneous with said opening step; decreasing fluid flowthrough said fluid flow passage simultaneous with said closing step. 22.A drill bit comprising: a drill bit body; a pressure relief nozzleinstalled into said drill bit body, said pressure relief nozzlecomprising hollow nozzle body having an upper end, a lower end, and aninterior passage connecting said upper end to said lower end anddefining a fluid flow path for fluid flowing through said interiorpassage; a flow control member located in said fluid flow path, saidflow control member movable between a first position and a secondposition, dependent upon a difference in fluid pressure of said fluid atsaid upper end and said lower end of said nozzle body.
 23. The drill bitof claim 22, further comprising: a second pressure relief nozzleinstalled into said drill bit body, said second pressure relief nozzlecomprising, hollow nozzle body having an upper end, a lower end, and aninterior passage connecting said upper end to said lower end anddefining a fluid flow path for fluid flowing through said interiorpassage; a flow control member located in said fluid flow path, saidflow control member movable between a first position and a secondposition, dependent upon a difference in fluid pressure of said fluid atsaid upper end and said lower end of said nozzle body for said secondpressure relief nozzle.
 24. The drill bit of claim 22, said firstposition being a fully open position and said second position being afully closed position.
 25. The drill bit of claim 22, said flow controlmember being a plug inserted in said nozzle body.
 26. The drill bit ofclaim 22, said flow control member moving linearly with respect to saidnozzle body to move from said first position to said second position.27. The drill bit of claim 22, said flow control member moving laterallywith respect to said nozzle body to move from said first position tosaid second position.
 28. The drill bit of claim 27, said flow controlmember including a ramp.
 29. The drill bit of claim 27, said flowcontrol member including a sliding ramp.
 30. The drill bit of claim 27,said flow control member including a first ramp and a second ramp. 31.The drill bit of claim 27, said flow control member including a firstsliding ramp and a second sliding ramp.
 32. The drill bit of claim 22,said first position allowing fluid flow through said pressure reliefnozzle and said second position not allowing fluid flow through saidpressure relief nozzle.
 33. The drill bit of claim 22, said firstposition defining a first diameter for said interior passage and saidsecond position defining a second diameter for said interior passage,said first diameter being larger than said second diameter.
 34. Thedrill bit of claim 22, said flow control member being repeatedly movablefrom said first position to said second position, and from said secondposition to said first position.
 35. The drill bit of claim 22, saiddrill bit further comprising a second nozzle, said second nozzle havinga hollow nozzle body with an upper end and a lower end connected by aflow path, there being a difference in fluid pressure between said upperend of said second nozzle and said lower end of said second nozzle, saidflow path of said second nozzle having a constant flow area regardlessof said pressure difference between said upper end of said second nozzleand said lower end of said second nozzle.